U.S. Pat. Re. No. 30,782 discloses unique fibrous webs, and unique methods for preparing fibrous webs, that carry a persistent electric charge. These methods involve fibrillating an electrically charged film and collecting the fibers into persistently charged webs that have special value as filters and for other purposes.
These unique webs would have further value if they were flame-retardant as well as electrically charged. However the conventional addition of a particulate flame-retardant agent into the film to be fibrillated makes a less persistently charged product. Maintenance of a persistent charge requires that the film be electrically insulating, but particulate additives such as flame-retardant agents tend to be electrically conducting and to take away the necessary electrically insulating state. In general this problem arises with the addition of any particulate material to the electrically charged fibrous webs, such as coloring pigments, anti-oxidants, stabilizers against ultraviolet light, and particles that make the film more readily fibrillated.